Bump I/O contact for semiconductor device

ABSTRACT

A bump contact electrically connects a conductor on a substrate and a contact pad on a semiconductor device mounted to the substrate. The first end of an electrically conductive pillar effects electrical contact and mechanical attachment of the pillar to the contact pad with the pillar projecting outwardly from the semiconductor device. A solder crown reflowable at a predetermined temperature into effecting electrical contact and mechanical attachment with the conductor is positioned in axial alignment with the second end of the pillar. A diffusion barrier electrically and mechanically joins the solder bump to the second end of the pillar and resists electro-migration into the first end of the solder crown of copper from the pillar. One diffusion barrier takes the form of a 2-20 micron thick control layer of nickel, palladium, titanium-tungsten, nickel-vanadium, or tantalum nitride positioned between the pillar and the solder crown.

BACKGROUND

A. Technical Field

The present invention relates generally to contacts for electricallyconnecting a substrate and a semiconductor device mounted to thesubstrate. More particularly, the present invention pertains to the bumpcontacts that are employed in the flip-chip packaging of semiconductordevices to electrically couple contact pads on a semiconductor devicewith a substrate to which the semiconductor device is mounted.

B. Background of the Invention

Bump contacts streamline the packaging of semiconductor devices byeliminating the use of electrical leads to connect each of the numerouscontact pads on a semiconductor device to corresponding conductors on asupport substrate to which the semiconductor device is mounted. Neitherthe gossamer quality of such electrical leads, nor the substantialnumber required in order to effect necessary electrically communicationsfor even a single semiconductor device, are optimally suited toefficient industrial manufacturing processes.

Furthermore, a bump contact between a contact pad on a semiconductordevice and conductor on a support substrate reduces dramatically theelectrical distance between the contact pad and the conductor relativeto that attainable using an electrical lead. In contrast with suchelectrical leads, a bump contact has only a single end at whichattachment is required, and attachment effected through bump contactsare considerably more mechanically robust than the attachments thatarise at either of an electrical lead.

SUMMARY OF THE INVENTION

The present invention embraces refinements in the packaging ofsemiconductor devices. The use of the present invention results insemiconductor packages that exhibit enhanced mechanical and electricalreliability.

According to one aspect of the present invention, an improved bumpcontact is provided with which to electrically connect a conductor on asubstrate to a contact pad on a semiconductor device mounted to thesubstrate.

The present invention also involves methods for making electricalconnections between contact pads on a semiconductor device andconductors on a support substrate to which the semiconductor device ismounted.

Certain features and advantages of the invention have been generallydescribed in this summary section; however, additional features,advantages, and embodiments are presented herein or will be apparent inview of the drawings, specification, and claims hereof. Accordingly, itshould be understood that the scope of the invention is not to belimited by the particular characterizations presented in this summarysection.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to exemplary embodiments of the present inventionthat are illustrated in the accompanying figures. Those figures areintended to be illustrative, rather than limiting. Although the presentinvention is generally described in the context of those embodiments, itis not intended by so doing to limit the scope of the present inventionto the particular features of the embodiments depicted and described.

FIG. 1 is a schematic elevation view of a semiconductor package thatincludes a semiconductor device, a support substrate, and a pair of bumpcontacts therebetween;

FIG. 2 is an enlarged schematic elevation view of a single of the bumpcontacts of FIG. 1 revealing additional structural aspects of thesemiconductor package of FIG. 1;

FIGS. 3A and 3B are enlarged diagrammatic depictions of a portion of theinterface between the materially-contrasting pair of major components ofthe bump contact of FIG. 2, illustrating conditions arising at thatinterface, initially upon completion of the manufacture of thesemiconductor package of FIG. 1, and subsequently after a period of use;

FIGS. 4A-4J are an ordered sequence of schematic elevation views ofsteps in a first method using teachings of the present invention toeffect an electrical connection between a conductor on a supportsubstrate and a contact pad on a semiconductor device mounted on thesupport substrate;

FIGS. 5A-5E are an ordered sequence of schematic elevation views ofsteps in a second method using teachings of the present invention toeffect an electrical connection between a conductor on a supportsubstrate and a contact pad on a semiconductor device mounted on thesupport substrate;

FIGS. 6A-6C are an ordered sequence of schematic elevation views ofsteps in a third method using teachings of the present invention toeffect an electrical connection between a conductor on a supportsubstrate and a contact pad on a semiconductor device mounted on thesupport substrate;

FIGS. 7A and 7B together present a single, comprehensive flow chart ofsteps in methods of manufacture illustrated, respectively in FIGS.4A-4J, in FIGS. 5A-5E, and in FIGS. 6A-6C;

FIG. 8 is a highly enlarged diagrammatic depiction of the interfacebetween the materially-contrasting pair of major components of a bumpcontact embodying teachings of the present invention;

FIGS. 9A and 9B are photomicrographs of bump contacts manufacturedwithout benefit of teachings of the present invention that togetheroffer an understanding of the material and structural alterationsproduced by electrical current in such bump contacts, FIG. 9A being aphotomicrograph of a newly-manufactured bump contact not embodyingteachings of the present invention, and FIG. 9B being a photomicrographof such a bump contact following a predetermined period of use;

FIGS. 10A and 10B are photomicrographs of bump contacts manufacturedaccording to teachings of the present invention that together, and bycomparison with FIGS. 9A and 9B, offer an understanding of thebeneficial reduction occasioned by the present invention in the materialand structural alterations caused in such bump contacts by electricalcurrent, FIG. 10A being a photomicrograph of a newly-manufactured bumpcontact embodying teachings of the present invention, and FIG. 10B beinga photomicrograph of such a bump contact following a predeterminedperiod of use; and

FIG. 11 is highly enlarged photomicrograph of a control layer embodyingthe inventive technology interposed between the materially-contrastingpair of major components of a bump contact following a predeterminedperiod of use.

In the present instance, it has been concluded that the cross hatchingtraditionally employed in the past in depicting cross-sectionalsemiconductor structures in figures would serve only to obscure, ratherthan to enhance, the understanding to be communicated herein of thepresent invention. Accordingly, in lieu of such traditional practices,cross-sectional cross hatching of structures has been foregone in theabove-described figures, and all structures depicted therein have beenscrupulously and even redundantly identified by reference characters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for purpose of explanation, specificdetails are set forth in order to provide an understanding of thepresent invention. The present invention may, however, be practicedwithout some or all of these details. The embodiments of the presentinvention described below may be incorporated into a number of differentelectrical components, circuits, devices, and systems. Structures anddevices shown in block diagram are illustrative of exemplary embodimentsof the present invention and are not to be used as a pretext by which toobscure broad teachings of the present invention. Connections betweencomponents within the figures are not intended to be limited to directconnections. Rather, connections between components may be modified,reformatted, or otherwise changed by intermediary components.

When the specification makes reference to “one embodiment” or to “anembodiment” it is intended mean that a particular feature, structure,characteristic, or function described in connection with the embodimentbeing discussed is included in at least one contemplated embodiment ofthe present invention. Thus, the appearance of the phrase, “in oneembodiment,” in different places in the specification does notconstitute a plurality of references to a single embodiment of thepresent invention.

FIG. 1 depicts basic elements of a typical semiconductor package. There,a semiconductor package 10 is shown that includes a support substrate 12having an engagement surface 14 to which is mounted a semiconductordevice 16. Semiconductor device 16 has an electrical access surface 18that is positioned parallel to and facing engagement surface 14 ofsupport substrate 12. Substantially identical bump contacts 20 extendbetween electrical access surface 18 of semiconductor device 16 andengagement surface 14 of support substrate 12, electrically couplingsemiconductor device 16 with support substrate 12.

Each bump contact 20 includes a pair of materially-contrasting majorcomponents. The first of these major components of bump contact 20 is anelectrically conductive pillar 22. Pillar 22 is attached at a first end24 thereof to electrical access surface 18 of semiconductor device 16 insuch a manner that pillar 22 projects outwardly from electrical accesssurface 18 toward engagement surface 14 of support substrate 12. On thefree or opposite second end 26 of pillar 22 is located the second majorcomponent of bump contact 20, a solder crown that is reflowable at apredetermined temperature into bridging any gap between second end 26 ofpillar 22 and engagement surface 14 of support substrate 12. As shown inFIG. 1, to bridge that gap the solder crown at second end 26 of pillar22 has assumed the form of a reflowed solder crown 28.

The space not occupied by bump contacts 20 between electrical accesssurface 18 of semiconductor device 16 and engagement surface 14 ofsemiconductor device 16 is packed by an adhesive fill 30. Adhesive fill30 enhances the mutual purchase between support substrate 12 andsemiconductor device 16, supports the structural integrity of each bumpcontact 20, and electrically insulates signals on one bump contact 20from signals on all other bump contacts 20.

FIG. 2 is an enlarged view of a single bump contact 20 from FIG. 1 thatreveals additional structural aspects of semiconductor package 10.

Initially, it can be appreciated from FIG. 2 that first end 24 of pillar22 does not directly engage electrical access surface 18 ofsemiconductor device 16. Rather, electrical access surface 18 carries acontact pad 32 that communicates electrically in manners not illustratedwith appropriate structures in semiconductor device 16. Pillar 22 ofbump contact 20 then actually effects direct electrical contact andmechanical attachment with contact pad 32.

A similar structural arrangement is apparent at the opposite end of bumpcontact 20. FIG. 2 reveals that reflowed solder crown 28 of bump contact20 does not directly engage electrical access surface 18 of supportsubstrate 12. Instead, electrical access surface 18 carries a conductor34 that communicates electrically in manners not illustrated withappropriate structures in support substrate 12. Reflowed solder crown 28of bump contact 20 then actually effects direct electrical contact andmechanical attachment with conductor 34.

In the vicinity of reflowed solder crown 28, the surface of conductor 34may be provided with a thin flux coating 36 that facilitates reflowedsolder crown 28 in achieving an electrical contact and a mechanicalattachment to conductor 34. Nonetheless, even when a coating, such asflux coating 36, is employed, the electrical contact and the mechanicalattachment thusly effected through the flux coating by a reflowed soldercrown will be considered, and will be referred to herein, as oneeffected directly between the reflowed solder crown and the conductor,as if the flux coating were not present.

Reflowed solder crown 28 extends between a first end 38, which isattached to second end 26 of pillar 22, and a reflow end 40 remotetherefrom. The antecedent material from which reflowed solder crown 28ultimately comes to be comprised is initially attached only to secondend 26 of pillar 22 and, being free of attachment to any otherstructure, is thus secured to what could be considered the tip of bumpcontact 20. During the assembly of the components of semiconductorpackage 10 shown in FIG. 2, this antecedent material at the tip of bumpcontact 20 is placed in proximity to conductor 34 and heated to apredetermined temperature that is sufficient to cause the antecedentmaterial to soften. While the portion of that antecedent material thatis attached to second end 26 of pillar 22 remains so attached to becomefirst end 38 of reflowed solder crown 28, the balance of theheat-softened antecedent material sags away from second end 26 of pillar22 toward and into contact with conductor 34, ultimately assuming theshape of reflow end 40 of reflowed solder crown 28.

Of significance to the present invention, is the region of bump contact20 in the vicinity of an interface 42, where second end 26 of pillar 22contacts first end 38 of reflowed solder crown 28. A portion ofinterface 42 at the right edge of bump contact 20 is shown in enlargeddetail in FIGS. 3A and 3B. Adhesive fill 30 has been omitted forconvenience to the right of bump contact 20 in FIGS. 3A and 3B.

FIGS. 3A and 3B illustrate with clarity selected problematic materialand structural alterations that have been discovered to arise in thevicinity of an interface, such as interface 24. These structuralalterations occur as a result of the contrasting material qualities ofthe metals from which a pillar, such as pillar 22, is constructed andthe metallic alloy constituents commonly contained in the solder of anabutting structure, such as reflowed solder crown 28.

Some of the structural alterations arise naturally, either duringmanufacture, or merely due to the contrasting qualities of differentmaterials placed in permanent contact in a structure. For the purpose ofthe discussion of the present invention, such natural structuralalterations do not significantly impair the reliability or thefunctionality of a bump contact, and are, therefore, considered to bebenign. Nonetheless, yet additional structural alterations are caused bythe intended transmission of electric current through a bump contactsduring use. Not all of such current-induced structural alterations aresimilarly benign; rather many are highly problematic. The presentinvention is directed toward the prevention of such problematiccurrent-induced structural alterations in a bump contact, such as bumpcontact 20.

In FIG. 3A, interface 42 is shown between second end 26 of pillar 22 andfirst end 38 of reflowed solder crown 28 immediately following themanufacture of bump contact 20. The contrasting material qualities ofthe metals from which pillar 22 is constructed and the metallic alloyconstituents commonly contained in abutting reflowed solder crown 28have given rise already to various natural structural alteration in bumpcontact 20 that are, nonetheless, considered to be benign. One of thesebenign natural structural alterations will be investigated beforeproceeding to FIG. 3B.

A pillar, such as pillar 22 of bump contact 20, is most commonly madefrom copper (Cu), and occasionally from gold (Au). The solder used in asolder crown, such as reflowed solder crown 28 of bump contact 20, is afusible tin-based alloy comprised primarily of tin (Sn) and lead (Pb)combined with various other metallic elements, such as antimony (Sb),bismuth (Bi), and silver (Ag). Lead-free solder compositions exist inwhich tin (Sn) predominates in combination with various traces ofantimony (Sb), bismuth (Bi), and silver (Ag). In FIGS. 3A and 3B, itwill be assumed for the purposes of discussion that pillar 22 iscomprised of copper (Cu) and that reflowed solder crown 28 is comprisedof a lead-free solder in which tin (Sn) is the major constituent.

At interface 42 of copper (Cu) in pillar 22 with tin (Sn) in reflowedsolder crown 28 a natural diffusion ND_(Cu) shown by arrows occurs ofcopper (Cu) out of pillar 22, across interface 42, and into theimmediately adjacent portions of reflowed solder crown 28. As a result,a commingled intermetallic compound phase 43 developed inadvertentlywithin the material matrix of reflowed solder bump 20 in reflowed soldercrown 28 adjacent to interface 42. Commingled intermetallic compoundphase 43 has a relatively uniform thickness T₄₃ measured into reflowedsolder crown 28 normal to interface 42. Commingled intermetalliccompound phase 43 extends into reflowed solder crown 28 to an irregularboundary that is shown in phantom in FIG. 3A by way of convenience as alinear lower edge 44. Lower edge 44 of commingled intermetallic compoundphase 43 is located in close proximity to interface 42.

Commingled intermetallic compound phase 43 is composed of copper (Cu)from pillar 22 that is distributed through the tin (Sn) in the solder ofreflowed solder crown 28. That copper (Cu) diffused into reflowed soldercrown 28 due to the heat imposed at interface 42, when the antecedentsolder material of reflowed solder crown 28 was applied to pillar 22during manufacture, as well as thereafter simply due to the permanentcontact of a region of copper (Cu) with a region of tin (Sn) in astructure, such as bump contact 20. When thusly developed, commingledintermetallic compound phase 43 is stable in size, representing in theextent thereof a state of atomic crystalline equilibrium establishedbetween pillar 22 and reflowed solder crown 28. The presence ofcommingled intermetallic compound phase 43 at the size shown in FIG. 3Acauses no significant adverse changes in the mechanical brittleness orin the electrical resistance of bump contact 20.

That equilibrium is, however, disrupted by the use of bump contact 20 toconduct electric current, or by the exposure of bump contact 20 afreshto extremes of high temperature. The consequences of such a disruptionof equilibrium in commingled intermetallic compound phase 43 aredepicted in FIG. 3B. Some of those consequences can be sufficientlysevere as to lead to catastrophic structural failure in bump contact 20.

In FIG. 3B, an electric current I₂₀ is shown schematically by an arrowto be flowing through bump contact 20 from pillar 22 and semiconductordevice 16 to reflowed solder crown 28 and support substrate 12. Aselectric current I₂₀ traverses interface 42, commingled intermetalliccompound phase 43 becomes unstable in size. This leads to furthermaterial and structural alterations in the vicinity of interface 42 thatdegrade the electrical and mechanical performance of bump contact 20.Fresh and undesirable intermetallic compound phases form in the vicinityof interface 42 that exhibit counter-functional electrical andmechanical properties. Some of these undesirable intermetallic compoundphases even encompass voids in the material matrix of bump contact 20 inthe vicinity of interface 42

According to teachings of the present invention, when bump contact 20 isused to transmit electrical current I₂₀, a rapid and substantial induceddiffusion ID_(Cu) shown by arrows occurs of copper (Cu) from pillar 22across interface 42 into commingled intermetallic compound phase 43 inreflowed solder crown 28. Commingled intermetallic compound phase 43enlarges. Lower edge 44 thereof moves deep into reflowed solder crown 28in the manner suggested in FIG. 3B by the dimension line associated withthickness T₄₃ of commingled intermetallic compound phase 43.

Eventually, commingled intermetallic compound phase 43 becomes saturatedwith copper (Cu) and is unable to grow further. The continuedtransmission of electrical current I₂₀ through bump contact 20 thencommences a counter-diffusion of tin (Sn) out of commingledintermetallic compound phase 43 in reflowed solder crown 28, acrossinterface 42, and into pillar 22, in an induced diffusion ID_(Sn)indicated by arrows in FIG. 3B.

Under these circumstances, the formation occurs of undesirableintermetallic compound phases of copper (Cu) and tin (Sn) that, unlikecommingled intermetallic compound phase 43, do exhibit both brittlematerial properties and increased resistance to the transmission ofelectrical current I₂₀.

The formation of brittle intermetallic compound phases significantlyreduces thermo-mechanical fatigue resistance and mechanical shockresistance, causing premature cracking in the vicinity of interface 42and reducing the structural reliability of bump contact 20. Increasedelectrical resistance in these intermetallic compound phases leads tounreliability in the electrical functioning of bump contact 20 as aninterconnection. Secondarily, higher electrical resistance in bumpcontact 20 causes any electrical current I₂₀ transmitted therethrough togenerate substantial heat in the material matrix of bump contact 20 inthe vicinity of interface 42. In the manner of a positive feedback, thisaccelerates the formation of undesirable intermetallic compound phases.

These undesirable intermetallic compound phases are not uniformlydistributed throughout bump contact 20, or segregated from each other.Nonetheless, for the sake of clarity, in FIG. 3B the main types ofobjectionable intermetallic compound phases are depicted in segregatedstrata.

The first of these strata is a commingled intermetallic compound phase45 that develops adjacent to interface 42 in pillar 22 and that iscomprised of tin (Sn) distributed through copper (Cu). Unfortunately,commingled intermetallic compound phase 45 is undesirably brittle andundesirably resistant to the transmission of electrical current I₂₀.

A second stratum of an objectionable intermetallic compound phase thatalso arises in bump contact 20 from use. Thus depicted is an evacuatedintermetallic compound phase 46 that is develops adjacent to interface42 in reflowed solder crown 28. Evacuated intermetallic compound phase46 encompasses a plurality of fine voids 48. Voids 48 arise when tin(Sn) in commingled intermetallic compound phase 43 in reflowed soldercrown 28 diffuses on an extended basis across interface 42 into pillar22. Evacuated intermetallic compound phase 46 develops subsequently tothe establishment of commingled intermetallic compound phase 45 inpillar 22 due to induced diffusion ID_(Sn) of tin (Sn) out of commingledintermetallic compound phase 43

The presence of voids 48 in evacuated intermetallic compound phase 46impairs the reliability of bump contact 20 in two ways. First, voids 48render evacuated intermetallic compound phase 46 mechanically brittle.Second, voids 48 physically diminish the electrically-conductivecross-sectional area of bump contact 20 at interface 42. This increaseselectrical resistance and, correspondingly, accelerates the rate ofheating in the material matrix of bump contact 20 that is associatedwith the transmission of electrical current I₂₀.

According to one aspect of the present invention, a bump contact, suchas bump contact 20 illustrated in FIGS. 3A and 3B, is provided withstabilization means for retarding the formation of a brittleintermetallic compound phase in the vicinity of interface 42 duringoperation of the semiconductor package in which bump contact 20 isemployed. The structure performing this function is located betweensecond end 26 of pillar 22 and first end 38 of reflowed solder crown 28and is disposed there when bump contact 20 is being manufactured.

By way of example, one form of a stabilization means according toteachings of the present invention takes the form of a barrier to theelectro-migration into first end 38 of reflowed solder crown 28 of aselected chemical constituent of pillar 22. Most commonly that selectedchemical constituent of pillar 22 is copper (Cu), or occasionally gold(Au). According to the present invention, the barrier is a control layerof material interposed between second end 26 of pillar 22 and first end38 of reflowed solder crown 28. The material of the barrier is chosenfrom the group consisting of nickel (Ni), palladium (Pd), tantalumnitride (TaN), alloys of titanium-tungsten (Ti—W), and alloys ofnickel-vanadium (Ni—V). The thickness of the control layer is notsubstantial, preferably in a range of from about 5 microns to about 10microns.

An exemplary first method by which such a control layer can bemanufactured in a bump contact, such as bump contact 20, and then usedin effecting an electrical connection between a support substrate and asemiconductor device mounted on the support substrate, will be describedby reference to the ordered sequence of schematic elevation viewspresented in FIGS. 4A-4J.

In FIG. 4A, a semiconductor device 50 is shown, and electrical accesssurface 52 thereof is identified. On electrical access surface 52 restsa contact pad 54 that communicates electrically in manners notillustrated with appropriate structures in semiconductor device 50. Tocommence making an electrical connection between contact pad 54 and asupport substrate to which semiconductor device 50 is to be mounted,electrical access surface 52 and contact pad 54 are covered with aphotoresist layer 56. As illustrated in FIG. 4B, a well 58 is formedthrough photoresist layer 56 to contact pad 54.

In FIG. 4C construction commences of a bump contact that is electricallyand mechanically attached to contact pad 54. The bottom of well 58 isfilled with a material, such as copper (Cu) or gold (Au), to produce anupstanding pillar 60 on contact pad 54. Pillar 60 as a result has anexposed end surface 61 that is accessible by way of well 58.

Then, as shown in FIG. 4D, a control layer 62 is applied through well 58to exposed end surface 61 of pillar 60. This is accomplished by way ofexample and not limitation using a method selected from the groupconsisting of electrolytic plating, electroless plating, and vapordeposition. Control layer 62 is made from a material capable ofresisting the electro-migration of one or more selected chemicalconstituents out of pillar 60 into the portions of the bump contactbeing manufactured in well 58 and that are to be added to the bumpcontact in subsequent steps of manufacturing. By way of example and notlimitation, control layer 62 is intended to resist the electro-migrationof copper (Cu) out of pillar 60. Correspondingly then, by way of exampleand not limitation, the material of control layer 62 is chosen from thegroup consisting of nickel (Ni), palladium (Pd), tantalum nitride (TaN),alloys of titanium-tungsten (Ti—W), and alloys of nickel-vanadium(Ni—V).

The thickness T₆₂ of control layer 62 must be sufficient to achieve theintended purpose thereof. By way of example, therefore, thickness T₆₂ ofcontrol layer 62 ranges from as little as about 2 microns to as much asabout 20 microns. A greater thickness T₆₂ in control layer 62 would notnecessarily derogate from the intended function of control layer 62, butmight be undesirable for reasons related to manufacturing methodology orto the architecture of the semiconductor package being constructed.Alternatively, by way of example, the thickness T₆₂ of control layer 62ranges from about 3.5 microns to about 15 microns, or more narrowly fromabout 5 microns to about 10 microns.

Then as shown in FIG. 4E, a reflowable solder crown 64 is installed oncontrol layer 62 using solder plating techniques. Other techniques ofinstallation are acceptable, and an additional such technique will beillustrated subsequently. Typically, the solder from which reflowablesolder crown 64 is made is a fusible tin-based alloy comprised primarilyof tin (Sn) and lead (Pb) in combination with various other metallicelements, such as antimony (Sb), bismuth (Bi), and silver (Ag).Lead-free solder compositions exist and are acceptable for use informing reflowable solder crown 64. In these, tin (Sn) predominates incombination with various traces of, for example, antimony (Sb), bismuth(Bi), copper (Cu), silver (Ag), and others. The collective assemblage ofpillar 60, control layer 62, and reflowable solder crown 64 will bereferred to hereinafter as a bump contact 66, notwithstanding thatfurther modifications to the structure of bump contact 66 will beimplemented before bump contact 66 is actually used in electricallyconnecting semiconductor device 50 to a support substrate.

As shown in FIG. 4F, all remaining portions of photoresist layer 56 areremoved from electrical access surface 52 of semiconductor device 50,leaving bump contact 66 as a free-standing structure that projects fromsemiconductor device 50 substantially normal to electrical accesssurface 52 thereof. Optionally, but as illustrated in FIG. 4G, theentirety of semiconductor device 50, including in particular bumpcontact 66, is warmed by ambient heating sufficiently to soften thesolder of reflowable solder crown 64 and allow reflowable solder crown64 to reform into a rounded reflowable solder crown 68.

FIG. 4H depicts a support substrate 72 to which semiconductor device 50from FIG. 4G is to be mounted and electrically connected. Engagementsurface 74 of support substrate 72 is also identified. Engagementsurface 74 carries a conductor 76, which is surmounted by a flux coating78. Conductor 76 communicates electrically in manners not illustratedwith appropriate structures in support substrate 72. Semiconductordevice 50 is positioned in proximity to support substrate 72 with bumpcontact 20 between semiconductor device 50 and support substrate 72 andwith rounded reflowable solder crown 68 contacting conductor 76 onsupport substrate 72.

As shown in FIG. 4I, the entire assemblage of support substrate 72 andsemiconductor device 50 is warmed sufficiently to soften the solder ofrounded reflowable solder crown 68 and allow rounded reflowable soldercrown 68 to achieve a reflow attachment electrically and mechanically onbehalf of bump contact 20 with conductor 76 on support substrate 72. Asthusly reconfigured the solder assumes the form of reflowed solder crown70.

Finally, as shown in FIG. 4J, adhesive fill 82 is used to pack the spacenot occupied by bump contact 66 between electrical access surface 52 ofsemiconductor device 50 and engagement surface 74 of semiconductordevice 72. A completed semiconductor package 84 results.

A second exemplary method for effecting an electrical connection betweena support substrate and a semiconductor device mounted on the supportsubstrate is illustrate in the ordered sequence of schematic elevationviews presented in FIGS. 5A-5E. The second method uses solder ballattachment to install a reflowable solder crown on a control layer, suchas control layer 62 created in the first method. To the extentpracticable, reference characters from that first method will beemployed to identify identical or substantially identical structuresappearing in the second method depicted in FIGS. 5A-5E.

Shown in FIG. 5A is semiconductor device 50 and contact pad 54 uponwhich some initial portions of a bump contact have been constructed.These initial portions of a bump contact include pillar 60 and controllayer 62 disposed thereon. In contrast to FIG. 4C in the first methoddisclosed earlier, an exposed surface 96 of control layer 62 is flushwith the top surface of photoresist layer 56.

As shown in FIG. 5B, a rounded solder ball 90 is installed on exposedsurface 96 of control layer 62, completing a bump contact 92.Photoresist layer 56 is removed as shown in FIG. 5C. Thereupon, as shownin FIG. 5D, semiconductor device 50 is positioned in proximity tosupport substrate 72 with bump contact 92 between semiconductor device50 and support substrate 72 and with solder ball 90 contacting conductor76 on support substrate 72.

The entirety of the assembly of support substrate 72 and semiconductordevice 50 shown in FIG. 5D is warmed sufficiently to soften the solderof solder ball 90 and allow solder ball 90 to achieve a reflowattachment electrically and mechanically on behalf of bump contact 92with conductor 76 on support substrate 72. As thusly reconfigured thesolder assumes the form of a reflowed solder crown 94 shown in FIG. 5E.Adhesive fill 82 is used to pack the space not occupied by bump contact92 between electrical access surface 52 of semiconductor device 50 andengagement surface 74 of support substrate 72. A completed semiconductorpackage 94 results.

A third exemplary method for effecting an electrical connection betweena support substrate and a semiconductor device mounted on the supportsubstrate is illustrate in the ordered sequence of schematic elevationviews presented in FIGS. 6A-6C. On a control layer, such as controllayer 62 created in the first method discussed above, the third methoduses a reflowable solder crown that exhibits no rounding whatsoever. Tothe extent practicable, reference characters from that first method willbe employed to identify identical or substantially identical structuresappearing in the third method depicted in FIGS. 6A-6C.

Shown in FIG. 6A is semiconductor device 50 and contact pad 54 uponwhich all portions of a bump contact 100 have been constructed. Theseportions include pillar 60, reflowable solder crown 64, and controllayer 62 sandwiched therebetween.

As shown in FIG. 6B, without further processing of the type depicted inFIG. 4G of the first method, semiconductor device 50 is positioned inproximity to support substrate 72 with bump contact 100 betweensemiconductor device 50 and support substrate 72 and with reflowablesolder crown 64 contacting conductor 76 on support substrate 72.

The entirety of the assemblage of support substrate 72 and semiconductordevice 50 shown in FIG. 6B is warmed sufficiently to soften the solderof reflowable solder crown 64 and allow reflowable solder crown 64 toachieve a reflow attachment electrically and mechanically on behalf ofbump contact 100 with conductor 76 on support substrate 72. As thuslyreconfigured the solder assumes the form of a reflowed solder crown 102shown in FIG. 6C. Adhesive fill 82 is used to pack the space notoccupied by bump contact 100 between electrical access surface 52 ofsemiconductor device 50 and engagement surface 74 of support substrate72. A completed semiconductor package 104 results.

FIGS. 7A and 7B together present a single, comprehensive flow chart ofsteps in the first method of manufacture illustrated in FIGS. 4A-4J, inthe second method of manufacture illustrated in FIGS. 5A-5E, and in thethird method of manufacture illustrated in FIGS. 6A-6C.

In FIG. 7A all of the methods commence with a shared set of steps thatare grouped conceptually in a dashed subroutine rectangle 110. Theoverall result of performing the steps included in subroutine rectangle110 is the construction of an electrically conductive pillar havingfirst and second extreme ends, as well as the attachment of the firstend of the pillar electrically and mechanically to a contact pad on asemiconductor device. In particular, those steps commence, as indicatedin process rectangle 112, by coating the contact pad and the surface ofthe semiconductor device carrying the contact pad with a photoresistlayer. Then as indicated in process rectangle 114, a well is formed inthe photoresist layer at the contact pad. Finally, as indicated inprocess rectangle 116, a material, such as copper (Cu) or gold (Au),from which to form the pillar of a bump contact is deposited in thebottom of the well.

In dashed subroutine rectangle 120, one of several alternative steps isthen undertaken. The result of performing any of the alternative stepswithin subroutine rectangle 120 is to apply to the second end of thepillar an electrically conductive control layer that is comprised of amaterial capable of resisting the electro-migration of copper (Cu) outof the second end of the pillar and into the reflowable solder crown.This overall objective is accomplished, either by electrolytic platingthat material as indicated in process rectangle 122, by electrolessplating that material as indicated in process rectangle 124, or by usingvapor deposition of that material as called for in process rectangle126.

Then in FIG. 7B, the methods resume in a dashed subroutine rectangle130, which encompasses a pair of alternative sub-subroutines, eachincluding a plurality of method steps. In one of the sub-subroutines oneof the method steps is optional. The overall result of performing eitherof the sub-subroutines within subroutine rectangle 130 is theinstallation of a reflowable solder crown on the control layer that wasapplied earlier to the second end of the pillar. This overall objectiveis accomplished, either by plating the material of the crown on thecontrol layer as set forth in finely-dashed sub-subroutine rectangle132, or by attaching the material of the crown on the control layer asset forth in finely-dashed sub-subroutine rectangle 134.

In the plating option of sub-subroutine rectangle 132, method stepscommence as indicted in process rectangle 136 by depositing a layer ofthe crown material on the control layer that was applied earlier to thesecond end of the pillar. Then as indicated in process rectangle 138,the photoresist layer is removed from the contact pad and the surface ofthe semiconductor device carrying the contact pad. Finally, the assemblyis heated to permit the layer of crown material to reflow into a roundedcrown, as set forth in process rectangle 140. The method step of processrectangle 140 is optional, however, as the remainder of the depictedmethod steps can be successfully preformed using a layer of crownmaterial that is not rounded.

In the attaching option of sub-subroutine rectangle 134, method stepscommence as indicted in process rectangle 142 by positioning a ball ofcrown material on the control layer that was applied earlier to thesecond end of the pillar. Then as indicated in process rectangle 144,the photoresist layer is removed from the contact pad and the surface ofthe semiconductor device carrying the contact pad.

Once a reflowable solder crown is installed on the control layer, asrequired in subroutine rectangle 130, the depicted methods resume in adashed subroutine rectangle 150, which encompasses a pair of alternativemethod steps. The alternative method step to be employed is determinedaccording to whether or not a rounded crown was produced in thepreceding method steps actually undertaken. The result of performingeither of the alternative method steps within subroutine rectangle 150is to position the semiconductor device in proximity to the supportsubstrate with the pillar between the semiconductor device and thesupport substrate and with the crown material contacting the conductoron the support substrate. If the crown produced in the preceding methodsteps is not rounded, then as indicated in process rectangle 152, theconductor is contacted by that layer of crown material. On the otherhand, if the crown produced in the preceding method steps is rounded,then as indicated in process rectangle 154, the conductor is insteadcontacted by that rounded crown material.

In FIG. 7B, all of the depicted methods conclude with a shared set ofsteps that are performed in sequence. First, as indicated in processrectangle 160, the assembly of the semiconductor device and the supportsubstrate with the pillar therebetween is heated sufficiently for thecrown to make a reflow attachment on behalf of the bump contactelectrically and mechanically with the conductor on the supportsubstrate. Then, as indicated in process rectangle 170, adhesive filleris applied to pack the space not occupied by the bump contact betweenthe semiconductor device and the support substrate. A completedsemiconductor package results that embodies teachings of the presentinvention.

FIG. 8 is a highly enlarged diagrammatic depiction of the interfaceregion between a materially-contrasting pair of major components in abump contact that embodies teachings of the present invention. Thusshown is a portion of a bump contact 180 located at and between anelectrically conductive pillar 182 constructed by way of example fromcopper (Cu) or gold (Au), and a reflowed solder crown 183 constructed ofa solder alloy containing tin (Sn). The end of pillar 182 not shown inFIG. 8 effects an electrical contact and a mechanical attachment onbehalf of one end of pillar 182 to a semiconductor device, which alsodoes not appear in FIG. 8. Similarly, the end of reflowed solder crown183 not shown in FIG. 8 effects an electrical contact and a mechanicalattachment on behalf of the opposite end of pillar 182 to a supportsubstrate, which is also missing in FIG. 8.

Located between the end 182 of pillar 182 that does appear in FIG. 8 andthe end 185 of reflowed solder crown 183 that does appear in FIG. 8 is acontrol layer 186 manufactured and configured according to teachings ofthe present invention. Control layer 186 serves as a barrier to retardthe diffusion of copper (Cu) from pillar 182 into reflowed solder crown183. In this manner, control layer 186, stabilizes the structural andelectrical properties of bump contact 180, notwithstanding the use ofbump contact 180 to transmit electrical current I₁₈₀, which isrepresented in FIG. 8 by an arrow. Therefore, control layer 186 isconstructed from a material chosen from the group consisting of nickel(Ni), palladium (Pd), tantalum nitride (TaN), alloys oftitanium-tungsten (Ti—W), and alloys of nickel-vanadium (Ni—V). Controllayer 186 has a thickness T₁₈₆ that ranges from about 5 microns to about10 microns.

Though relatively thin, control layer 186 necessarily has a first side187 that is secured to end 182 of pillar 182 and a second side 188 thatis secured to end 185 of reflowed solder crown 183. During thetransmission through bump contact 180 of electrical current I₁₈₀, thepresence of control layer 186 between pillar 182 and reflowed soldercrown 183 retards the migration displacement of copper (Cu) away fromthe original manufactured location thereof in pillar 182 and into end185 of reflowed solder crown 183. In this manner the formation isresisted within the material matrix of bump contact 180 of theundesirable intermetallic compound phases depicted, for example in FIG.3B. Thus, no commingled intermetallic compound phase comprised of tin(Sn) distributed through copper (Cu) develops in pillar 182, and noevacuated intermetallic compound phase containing voids develops inreflowed solder crown 183.

The remaining figures are photomicrographs of actual bump contactsextracted from assembled semiconductor packages and acquired afterdissection using a scanning electron microscope.

FIGS. 9A and 9B are photomicrographs of bump contacts manufacturedwithout benefit of teachings of the present invention. Taken togetherFIGS. 9A and 9B afford a visual understanding inter alia of theundesirable material and structural alterations produced by electricalcurrent in such bump contacts.

FIGS. 10A and 10B are photomicrographs of bump contacts manufactured andconfigured according to teachings of the present invention. Takentogether FIGS. 9A and 9B, afford a visual understanding of the dramaticreduction occasioned by the present invention in the undesirablematerial and structural alterations caused by electrical current in suchbump contacts. FIG. 11 is a highly-enlarged view of a portion of anotherbump contact embodying the present invention after sustained use.

FIG. 9A depicts an unused, newly-manufactured bump contact 190 a thatdoes not embody teachings of the present invention. Bump contact 190 aconnects a contact pad 192 on a semiconductor device 194 with aconductor 196 on a support substrate that is not included in FIG. 9A.Conductor 196 is surmounted by a flux coating 198. The space notoccupied by bump contact 190 a between semiconductor device 194 and thesupport substrate that carries conductor 196 is packed by an adhesivefill 200.

Bump contact 190 a includes a pair of materially-contrasting majorcomponents: an electrically conductive pillar 202 made of copper (Cu);and a reflowed solder crown 204 made of a lead-free solder alloycontaining primarily tin (Sn) and silver (Ag). By way of perspective,pillar 202 has a diameter measured across bump contact 190 a betweenregions of adhesive fill 200 that is equal to about 120 microns. Theheight of pillar 202 measured in alignment with bump contact 190 a fromcontact pad 192 to reflowed solder crown 204 is equal to about 80microns.

The abutment of pillar 202 against reflowed solder crown 204 defines aninterface 206 therebetween that is repeatedly identified in FIG. 9A. Apair of irregular, dark lines are shown extending across reflowed soldercrown 204 between regions of adhesive fill 200 to either side thereof inFIG. 9A. These are each a margin of a respective commingledintermetallic compound phase that was produced inadvertently within thematerial matrix of reflowed solder crown 204 during, respectively, themanufacture of bump contact 190 a and the attachment of bump contact 190a to conductor 196.

The first of these is a commingled intermetallic compound phase 208 thatdeveloped in reflowed solder crown 204 adjacent to interface 206.Commingled intermetallic compound phase 208 is composed of copper (Cu)from pillar 202 that is distributed through the metallic elements in thesolder of reflowed solder crown 204. That copper (Cu) diffused intoreflowed solder crown 204 due to the heat imposed at interface 206, whenthe antecedent solder material of reflowed solder crown 204 is appliedto pillar 202 during the manufacture of bump contact 190 a as astructure secured to semiconductor device 194. Commingled intermetalliccompound phase 208 causes no significant adverse changes in themechanical brittleness or in the electrical resistance of bump contact190 a.

The other commingled intermetallic compound phase is a commingledintermetallic compound phase 210 that developed in reflowed solder crown204 adjacent to flux coating 198 on conductor 196. Commingledintermetallic compound phase 210 is composed of copper (Cu) fromconductor 196 and tin (Sn) from flux coating 198 that are distributedthrough the metallic elements in the solder of reflowed solder crown204. That copper (Cu) and that tin (Sn) diffused into reflowed soldercrown 204 due to the heat imposed on conductor 196 and on flux coating198, when the antecedent solder material of reflowed solder crown 204was warmed sufficiently to enable the reflow attachment of bump contact190 a to conductor 196. Commingled intermetallic compound phase 210causes no significant adverse changes in the mechanical brittleness orin the electrical resistance of bump contact 190 a.

FIG. 9B depicts a bump contact 190 b that, like bump contact 190 a inFIG. 9A, does not embody teachings of the present invention. Bumpcontact 190 b and bump contact 190 a are not actually a single bumpcontact, but both were manufactured to the same specification using thesame materials in substantially identical manufacturing processes.Therefore, for the purpose of any practical comparisons, bump contact190 b and bump contact 190 a are structurally identical. To the extentpracticable, identical reference characters will be employed to identifycorresponding structures in bump contact 190 b and in bump contact 190a.

Unlike bump contact 190 a, however, bump contact 190 b is neithernewly-manufactured nor unused. Instead, bump contact 190 b was subjectedfor approximately 800 hours to the transmission therethrough of anelectrical current I₁₉₀ equal to about 0.5 amperes.

The use of bump contact 190 b in this way produced many changes in thematerial structure thereof. A few of these changes, which are relativelybenign to the overall material and electrical reliability of bumpcontact 190 b, will be discussed by giving initial attention to thecontrast in appearance between reflowed solder crown 204 in bump contact190 b in FIG. 9B and reflowed solder crown 204 in unused bump contact190 a in FIG. 9A.

For example, in bump contact 190 b commingled intermetallic compoundphase 208 is enlarged substantially, having extending itself frominterface 206 far into reflowed solder crown 204. Commingledintermetallic compound phase 210 also grew in extent, but lessdramatically, advancing somewhat into reflowed solder crown 204 fromconductor 196. The expansion of each was, however, faster toward theright edge of reflowed solder crown 204 than toward the left. Inaddition, the relatively uniform intermixture of tin (Sn) and silver(Ag) exhibited in reflowed solder crown 204 of bump contact 190 a inFIG. 9A was disrupted in localized regions by the diffusion of silver(Ag) away into other areas. Thus, a virtually pure region 212 of tin(Sn) developed on the left edge and in the center of reflowed soldercrown 204. The presence and the growth of pure region 212 and commingledintermetallic compound phases 208, 210 did not, however, lead tosignificant undesirable changes in mechanical brittleness or electricalresistance.

On the other hand, further comparison of bump contact 190 b in FIG. 9Bto bump contact 190 a in FIG. 9A does reveal additional material andelectrical changes that are quite objectionable.

First, a commingled intermetallic compound phase 214 of substantiallyuniform thickness developed in pillar 202 adjacent to interface 206.Intermetallic compound phase 214 is composed of tin (Sn) distributedthrough copper (Cu). Commingled intermetallic compound phase 214 arosedue to the transmission of electrical current I₁₉₀ across interface 206and a resulting counter-diffusion of tin (Sn) out of commingledintermetallic compound phase 210, across interface 206, and into pillar202. Unfortunately, commingled intermetallic compound phase 214, isundesirably brittle and undesirably resistant to the transmission ofelectrical current I₁₉₀.

Second, numerous fine voids 216 developed in reflowed solder crown 204adjacent to interface 206 in commingled intermetallic compound phase208. This had the effect of converting a portion of benign commingledintermetallic compound phase 208 into a problematic, evacuatedintermetallic compound phase 218. Voids 216 arose after substantialdisplacement of copper (Cu) from pillar 202 into commingledintermetallic compound phase 208 saturated reflowed solder crown 204with copper (Cu), and forced tin (Sn) from commingled intermetalliccompound phase 208 to counter-diffuse into pillar 202.

Voids 216 in evacuated intermetallic compound phase 218 impair thereliability of bump contact 190 b in two ways. First, voids 216 renderevacuated intermetallic compound phase 218 mechanically brittle. Second,voids 216 physically diminish the electrically-conductivecross-sectional area of bump contact 190 b in the vicinity of interface206. The increased electrical resistance correspondingly accelerates therate that bump contact 190 b is heated whenever electrical current I₁₉₀is transmitted.

FIG. 10A depicts an unused, newly-manufactured bump contact 220 a thathas been manufactured and is structures according to teachings of thepresent invention. Bump contact 220 a connects a contact pad 222 on asemiconductor device with a conductor 226 on a support substrate.Neither the semiconductor device nor the support substrate is includedin FIG. 10A. Conductor 226 is surmounted by a flux coating 228. Thespace not occupied by bump contact 220 a between the semiconductordevice and the support substrate is packed by an adhesive fill 230.

Bump contact 190 a includes a pair of materially-contrasting majorcomponents: an electrically conductive pillar 232 made of copper (Cu);and a reflowed solder crown 234 made of a lead-free solder alloycontaining primarily tin (Sn) and silver (Ag). By way of affording aperspective, a size scale using increments of 100 microns each isincluded on the lower right edge of FIG. 10A.

Located between pillar 232 and reflowed solder crown 234 is a controllayer 236 manufactured and configured according to teachings of thepresent invention. Control layer 236 is constructed from nickel (Ni),thereby to serve as a barrier to retard the diffusion of copper (Cu)from pillar 232 into reflowed solder crown 234. In this manner, controllayer 236, stabilizes the structural and electrical properties of bumpcontact 220 a, notwithstanding the use of bump contact 220 a to transmitelectrical current. Control layer 236 has a thickness T₁₉₀ that is atleast about 20 microns. Though relatively thin, control layer 236necessarily has a first side 238 that is secured to pillar 232 and asecond side 240 that is secured reflowed solder crown 234.

A commingled intermetallic compound phase was produced inadvertentlywithin the material matrix 242 of reflowed solder crown 234 of FIG. 10Aduring the attachment of bump contact 220 a to conductor 226.

That commingled intermetallic compound phase is a commingledintermetallic compound phase 244 that developed in material matrix 242of reflowed solder crown 204 adjacent to flux coating 228 on conductor226. Commingled intermetallic compound phase 244 is composed of copper(Cu) from conductor 226 and tin (Sn) from flux coating 228 that aredistributed through the metallic elements in the solder of reflowedsolder crown 234. That copper (Cu) and that tin (Sn) diffused intoreflowed solder crown 234 due to the heat imposed on conductor 226 andon flux coating 228, when the antecedent solder material of reflowedsolder crown 234 was warmed sufficiently to enable the reflow attachmentof bump contact 220 a to conductor 226. Commingled intermetalliccompound phase 244 caused no significant adverse changes in themechanical brittleness or in the electrical resistance of bump contact220 a.

FIG. 10B depicts a bump contact 220 b electrically and mechanicallyinterconnecting contact pad 222 on a semiconductor device 246 withconductor 226 on a support substrate 248. Like bump contact 220 a inFIG. 10A, bump contact 220 b embodies teachings of the presentinvention.

Bump contact 220 b and bump contact 220 a are not actually a single bumpcontact, but both were manufactured to the same specification using thesame materials in substantially identical manufacturing processes.Therefore, for the purpose of any practical comparisons, bump contact220 b and bump contact 220 a are structurally identical. To the extentpracticable, identical reference characters will be employed to identifycorresponding structures in bump contact 220 b and in bump contact 220a.

Unlike bump contact 220 a, however, bump contact 220 b is neithernewly-manufactured nor unused. Instead, bump contact 220 b was subjectedfor approximately 3700 hours to the transmission therethrough of anelectrical current I₂₂₀ equal to about 0.5 amperes.

The use of bump contact 220 b in this way produced only slight changesin the material structure thereof. One of these changes will, however,be discussed by giving initial attention to the contrast between theappearance of material matrix 242 of reflowed solder crown 234 in bumpcontact 220 b in FIG. 10B and the appearance of material matrix 242 ofreflowed solder crown 234 in unused bump contact 220 a in FIG. 10A.

For example, in bump contact 220 b commingled intermetallic compoundphase 244 grew in extent, advancing somewhat uniformly across bumpcontact 190 b into material matrix 242 of reflowed solder crown 234 fromconductor 226. The presence and the growth of commingled intermetalliccompound phase 244 did not, however, lead to significant undesirablechanges in mechanical brittleness or electrical resistance.

A further comparison of bump contact 220 b in FIG. 10B to bump contact220 a in FIG. 10A does not reveal significant objectionable material orelectrical changes of the types observed in bump contact 190 b of FIG.9B due to the transmission of electrical current I₁₉₀. The objectionablechanges produced in bump contact 190 b increased the brittleness and theelectrical resistance relative to those in unused bump contact 190 a.Tellingly, while electrical current I₁₉₀ transmitted through bumpcontact 190 b and electrical current I₂₂₀ transmitted through bumpcontact 220 b were equal in magnitude, the duration of currenttransmission through bump contact 220 a was more than four times greaterthat the duration of current transmission through bump contact 190 b.Still, no significant objectionable changes are detectable in bumpcontact 220 b.

During the transmission through bump contact 220 of electrical currentI₂₂₀, the presence of control layer 236 between pillar 232 and reflowedsolder crown 234 retarded the electrically-induced migrationdisplacement of copper (Cu) away from the original manufactured locationthereof within pillar 232 and into reflowed solder crown 234. In thismanner the formation was resisted within the material matrix of bumpcontact 220 of the undesirable intermetallic compound phases depicted,for example in FIG. 3B and in FIG. 9B. Thus, no commingled intermetalliccompound phase comprised of tin (Sn) distributed through copper (Cu)developed in pillar 232, and no evacuated intermetallic compound phasecontaining voids developed in reflowed solder crown 234.

As a further confirmation of these conclusions relative to the inventivetechnology, FIG. 11 presents a highly enlarged photomicrograph of aportion of the right edge of a bump contact 250 that has a nickel (Ni)control layer 252 embodying the inventive technology interposed betweenthe problematic materially-contrasting pair of major components of bumpcontact 250. Bump contact 250 was used for approximately 3700 hours totransmit an electrical current I₂₅₀ equal to about 0.5 amperes. By wayof perspective, a size scale using increments of 20 microns each isincluded on the lower right edge of FIG. 11. That size scale indicatesin effect that the magnification of the portion of bump contact 250 inFIG. 11 is approximately five times the magnification of bump contact190 b in FIG. 10B.

Shown as a result in FIG. 11 is a first face 254 of control layer 252.First face 254 of control layer 252 is abutted by a pillar 258 comprisedof copper (Cu). The face of control layer 252 on the side of controllayer 252 opposite from first face 254 is abutted by the tin (Sn) andsilver (Ag) solder alloy of a reflowed solder crown 260. Also appearingis an adhesive fill 262 that surrounds bump contact 250.

A commingled intermetallic compound phase was produced inadvertentlywithin the material matrix of reflowed solder crown 260 during themanufacture of bump contact 250. A thin commingled intermetalliccompound phase 256 developed in reflowed solder crown 204 adjacent tocontrol layer 252. Commingled intermetallic compound phase 256 iscomposed of nickel (Ni) from control layer 252 that is distributedthrough the metallic elements in the solder of reflowed solder crown260. That nickel (Ni) diffused into reflowed solder crown 260 due to theheat imposed on control layer 252, when the antecedent solder materialof reflowed solder crown 260 was applied to control layer 252 during themanufacture of bump contact 250 as a structure secured a semiconductordevice. Commingled intermetallic compound phase 256 causes nosignificant adverse changes in the mechanical brittleness or in theelectrical resistance of bump contact 250.

During the transmission through bump contact 200 of electrical currentI₂₅₀, it is apparent from FIG. 11 that the presence of control layer 252between pillar 258 and reflowed solder crown 260 retarded theelectrically-induced migration displacement of copper (Cu) from pillar258 into reflowed solder crown 260. In this manner the formation wasresisted within the material matrix of bump contact 250 of theundesirable intermetallic compound phases depicted, for example in FIG.3B and in FIG. 9B. Thus, no commingled intermetallic compound phasecomprised of tin (Sn) distributed through copper (Cu) developed inpillar 258, and no evacuated intermetallic compound phase containingvoids developed in reflowed solder crown 260.

The foregoing description of the invention has been described forpurposes of clarity and understanding. It is not intended to limit theinvention to the precise form disclosed. Various modifications may bepossible within the scope and equivalence of the appended claims.

1. A bump contact for electrically connecting a conductor on a substrateand a contact pad on a semiconductor device mounted to the substrate,the bump contact comprising: a. an electrically conductive pillar havingfirst and second extreme ends, the first end of the pillar being capableof effecting electrical contact and mechanical attachment of the pillarto the contact pad on the semiconductor device with the pillarprojecting outwardly from the semiconductor device; b. a solder crownhaving first and second extreme ends, the solder crown being positionedin axial alignment with the pillar with the first end of the soldercrown facing the second end of the pillar, the solder crown beingreflowable at a predetermined temperature into effecting electricalcontact and mechanical attachment by the second end thereof with theconductor on the substrate; and c. a diffusion barrier electrically andmechanically joining the first end of the solder bump to the second endof the pillar, the diffusion barrier resisting electro-migration intothe first end of the solder crown by a selected chemical constituent ofthe pillar, the diffusion barrier comprising a control layer of materialon the second end of the pillar, the material of the control layer beingchosen from the group consisting of palladium, alloys oftitanium-tungsten, and tantalum nitride.
 2. A bump contact as recited inclaim 1, wherein the selected chemical constituent of the pillarcomprises a material chosen from the group consisting of copper andgold.
 3. A bump contact as recited in claim 1, wherein, by resistingelectro-migration into the first end of the solder crown by a selectedchemical constituent of the pillar, the diffusion barrier simultaneouslyresists counter-diffusion into the second end of the pillar by aselected chemical constituent of the solder crown.
 4. A bump contact asrecited in claim 3, wherein the selected chemical constituent of thesolder crown comprises tin.
 5. A bump contact as recited in claim 1,wherein the diffusion barrier has a thickness measured between thesolder crown and the second end of the pillar, and the thickness of thediffusion barrier is in a range of from about 2 microns to about 20microns.
 6. A bump contact as recited in claim 1, wherein the soldercrown is tin-based.
 7. A semiconductor package comprising: a. a supportsubstrate having a engagement surface carrying an electrical conductorthereupon; b. a semiconductor device having an electrical access surfacebearing a contact pad through which the semiconductor devicecommunicates electrically with the conductor on the support substrate,the semiconductor device being seated on the substrate with theengagement surface of the semiconductor device facing the engagementsurface of the support substrate and the contact pad of thesemiconductor device closely opposing the conductor on the supportsubstrate; c. an electrically conductive pillar having first and secondextreme ends, the first end of the pillar being in electrical contactwith and mechanically attached to the contact pad on the semiconductordevice, the pillar thereby projecting from the engagement surface of thesemiconductor device toward the conductor on the support substrate; d. areflowed solder crown having first and second extreme ends, the soldercrown being in axial alignment with the pillar with the first end of thesolder crown facing the second end of the pillar and with the second endof the solder crown being in electrical contact and mechanicalattachment with the conductor on the support substrate; e. stabilizationmeans between the second end of the pillar and the first end of thesolder crown for retarding the growth at the second end of the pillar ofa brittle intermetallic phase formation during operation of thesemiconductor package; and wherein the stabilization means comprises acontrol layer of material interposed between the second end of thepillar and the first end of the solder crown, the material of thecontrol layer being chosen from the group consisting of palladium,alloys of titanium-tungsten, and tantalum nitride.
 8. A semiconductorpackage as recited in claim 7, wherein the stabilization means comprisesa barrier to the electro-migration into the first end of the soldercrown by a selected chemical constituent of the pillar.
 9. Asemiconductor package as recited in claim 8, wherein the selectedchemical constituent of the pillar comprises a material chosen from thegroup consisting of copper and gold.
 10. A semiconductor package asrecited in claim 8, wherein, by resisting electro-migration into thefirst end of the solder crown by a selected chemical constituent of thepillar, the diffusion barrier simultaneously resists counter-diffusioninto the second end of the pillar by a selected chemical constituent ofthe solder crown.
 11. A semiconductor package as recited in claim 10,wherein the selected chemical constituent of the solder crown comprisestin.
 12. A semiconductor package as recited in claim 7, wherein thecontrol layer has a thickness measured between the solder crown and thesecond end of the pillar, and the thickness of the control layer is in arange of from about 5 microns to about 10 microns.
 13. A method formaking an electrical connection between a conductor on a supportsubstrate and a contact pad on a semiconductor device mounted to thesupport substrate, the method comprising the steps: a. constructing anelectrically conductive pillar having first and second extreme ends; b.attaching the first end of the pillar electrically and mechanically tothe contact pad on the semiconductor device with the pillar projectingoutwardly from the semiconductor device; c. applying to the second endof the pillar an electrically conductive control layer comprised of amaterial capable of resisting electro-migration of copper out of thepillar through the second end thereof, wherein the control layer iscomprised a material chosen from the group consisting of palladium,alloys of titanium-tungsten, and tantalum nitride; d. installing areflowable solder crown on the side of the control layer opposite fromthe second end of the pillar; e. positioning the semiconductor device inproximity to the support substrate with the pillar between thesemiconductor device and the support substrate and with the solder crowncontacting the conductor on the support substrate; and f. heating thesolder crown sufficiently to cause reflow attachment of the solder crownelectrically and mechanically with the conductor on the supportsubstrate.
 14. A method as recited in claim 13, wherein in the step ofapplying an electrically conductive control layer, the material capableof resisting electro-migration of copper is applied to the second end ofthe pillar using a method selected from the group consisting ofelectrolytic plating, electroless plating, and vapor deposition.
 15. Amethod as recited in claim 13, wherein the reflowable solder crown isinstalled on the side of the control layer opposite from the second endof the pillar using a method selected from the group consisting ofsolder plating and solder ball attachment.
 16. A method as recited inclaim 13, wherein the wherein the control layer has a thickness measuredbetween the solder crown and the second end of the pillar, and thethickness of the control layer is at least about 2 microns.
 17. A bumpcontact for electrically connecting a substrate and a semiconductordevice mounted to the substrate, the bump contact comprising: a. anelectrically conductive pillar having first and second extreme ends, thefirst end of the pillar being capable of effecting electrical contactand mechanical attachment of the pillar to the semiconductor device withthe pillar projecting outwardly therefrom; b. a control layer disposedon the second end of the pillar; and c. a solder crown secured to thecontrol layer in axial alignment with the pillar, the solder crown beingreflowable at a predetermined temperature into effecting electricalcontact and mechanical attachment with the substrate; wherein thecontrol layer comprises a material chosen from the group consisting ofpalladium, alloys of titanium-tungsten, and tantalum nitride, and has athickness measured between the solder crown and the second end of thepillar; and the thickness of the control layer is more than 10 micronsto sufficiently retard formation of a brittle intermetallic compoundphase between the electrically conductive pillar and the solder crown.